So someone who “never matures” should never get married? Chas V’Shalom! The chiyuv to get married isn’t dependent on anyones feelings of “maturity”. Nor is Chazal’s sagely advice to get married at 18 or younger.
Far far better to get married very young straight out of the Beis Medrash or Beis Yaakov, before the negative influences start creeping in, then to wait to “mature”. Mature in shtuss and negative influences is what’s going to occur. Far more successful are the marriages of those who married very young (i.e. 18), then those who married later.